Drug delivery by inhalation is well known in the treatment of respiratory disorders, such as asthma. Inhalation has also found use in delivery of systemic drugs through the lungs, wherein the drugs are absorbed directly into the blood stream without having to pass through (and be broken down by) the digestive tract.
Ultra-fine, dry powders, also known as micro- and nano-powders, are the subject of increasing interest in pharmaceutical manufacturing, because they provide a solution to many of the shortcomings of blended drugs. Active drug ingredients are produced, packaged and administered to the patient as pure, dry powders, without blending them with solvents or other agents. Elimination of the blending steps simplifies the manufacturing process, reduces development and manufacturing costs, makes dosage more accurate, and extends the drug's shelf life.
Dry powder inhalers are known in the art, for delivery of dry powder medications to the lungs. For optimal penetration and absorption in the lungs, the powder particles should be particularly fine--on the order of 4 .mu.m in size, or less. The drawback of such ultra-fine, dry powders is that they are difficult to handle, tending to clump and stick in storage and to scatter when disturbed by even slight air movements. These handling problems must be overcome if dry powder drugs are to be used efficiently and safely, and special methods must be used for accurate dose processing and administration.
PCT patent publications WO 97/47346 and WO 97/47347, which are incorporated herein by reference, describe inhaler apparatus for use with fine powders. A dry powder inside the inhaler apparatus initially adheres to a substrate surface therein. When a patient using the apparatus inhales, an electrostatic field is triggered inside the inhaler. The field causes the powder to be lifted from the surface and drawn into the patient's mouth. To be handled in this manner, the powder must be pre-charged. For practical field intensities (in a hand-held device that is inserted in the patient's mouth), the amount of powder that can be delivered is limited. Furthermore, application of the field must be precisely timed relative to the patient's inhalation to avoid scattering the powder, and the air flow trigger required for this purpose is costly and complex.
MicroDose Technologies Inc., of New Jersey, offers a dry powder inhaler based on the general principles described in the above-mentioned PCT publications. In addition to the used of a timed electrostatic field, the MicroDose inhaler uses a piezoelectric vibrator, brought into contact with a blister pack containing the powder, to deaggregate the particles. The mechanical interface for transferring the vibrations to the powder in the pack is inefficient and further increases the cost and complexity of the inhaler.